As a conventional method for preparing p,p'-biphenol, a method is known which comprises using 2,6-di-t-butyl phenol (hereinafter referred to as 2,6B) as a chief raw material, allowing said material to be subjected to oxidative coupling in the presence of an alkaline catalyst to have 3,3',5,5'-tetra-t-butyl diphenoquinone produced followed by the reduction thereof with hydrogen to obtain 3,3',5,5'-tetra-t-butyl biphenol (hereinafter referred to as TBBP) and then debutylating the TBBP. See reference P.3.
As a method of debutylating TBBP, a method is disclosed in Japanese Patent Laid-open No. 1434/1984 to obtain p,p'-biphenol wherein TBBP isolated from an oxidation liquid is subjected to reaction by heating in the presence of phenol and activated clay for permitting the t-butyl group of TBBP to be transalkylated to the meta position of phenol.
In said method for preparing p,p'-biphenol, each of intermediates, 2,6B and TBBP is purified through isolation in the corresponding formation stage, and is used as the raw material for the following process. Each of the purification processes through isolation, therefore, necessitates its additional apparatus, and for the operation thereof some persons will be needed for process control and operations, in addition, resulting complicated operations will ineviably lead to decreased production efficiency.